We propose to perform a comprehensive qualitative and quantitative analysis at the light and electron microscope levels of: (1) the development of the cellular features of various neuron types in the visual cortex of the rat, and (2) the temporal and spatial characteristics of synaptogenesis in the same cortical area. Information on the development of this cortical structure where much of the processing of visual information takes place will be provided by these studies, which are, in any case, an essential prerequisite for studies designed to investigate the effects on the development of the visual cortex of various experimental, environmental, and genetic factors.